The purpose of this study is to test the feasibility and tolerability of donepezil in a small group of patients with anorexia nervosa (AN). Study participants will be receiving care at the New York State Psychiatric Institute Eating Disorders Unit. Study medication will be increased from 1 mg per day to a maximum of 5 mg per day for up to 8 weeks. Participants will be closely monitored for side effects by a research psychiatrist every week, in addition to the regular clinical monitoring they receive during inpatient treatment. The study will also include assessments of habit strength to measure any changes in maladaptive eating habits over the course of the treatment.